The long-term goal of this project is to understand early-onset familial Alzheimer's Disease (FAD) on a detailed molecular level by focusing on one family of proteins known to be mutated in the diseased state. Point mutations in presenilin-I (PS-I) have been shown to be responsible for an estimated 70% of the early-onset cases of FAD, with 38% of them located in exon 8 (the N-terminal portion of a 145 amino acid loop). The goal is to understand how these mutations lead to early-onset FAD. More specifically, the focus will be on how the mutant PS-I proteins are biochemically and structurally different from the wild type (wt) PS-I protein. As such, the following questions will be addressed: Do recombinant wild-type and mutant loop region PS-I proteins fold as stable modules that are amenable to structural studies? Do preliminary biophysical studies indicate that detailed three-dimensional NMR structural analysis will be feasible? To address these questions, the 145 amino acid wild-type PS-I loop, as well as four mutant PS-I loops, will be cloned and expressed as soluble proteins. 15N-HSQC NMR experiments, as well as CD studies, will determine whether these purified protein fragments fold as stable modules amenable to future 3-D structural characterization.